In last years I read a lot of publications about race engines. Many of authors, especially from US suggest to use a torque plate when we are reboring our engine block. A careful reader know that GC wrote in his 2010/2013 book, that using a torque plate is not a necessary.

This type of plate should "simulate" an assembled block with a head.

I am a person who like to know why solution is the best, and if I can do it personally I do it. So today I made a some test.

I assembled a 2L TC block with a cylinder head. Of corse, I used a new cylinderhead gasket too. I torqued bolts to OE spec (old type hexagonal bolts). All should works as normal engine when assembling it to work in a car.

Assembled "dummy" block.

20160715_194010.jpg (101.32 KiB) Viewed 7865 times

I made a lot of measurements of bores, record it, I made this the same way as we should to do it when we inspecting an engine block. I measured it across and inline of block. I done a really lot of measurements to avoid any error with it (unfortunely I done this test on an used block, a quite more
requiring attention especially if we want do it really precisely.

I used for it my Mitutoyo Bore Gauge with digital indicator, in my opinion this is the best tool for it.

This is a 84.047mm

20160715_203135.jpg (78.73 KiB) Viewed 7865 times

I checked my measurements before and after assembly block with head and I get this conclusion.

As GC wrote, we musn't use a torque plate. A dimensions that I get before and after are quite similar, about 0,002-0,004mm difference which is a certainly a measurement slip (I don't know how I should called in english but I think everybody know what I mean).

I will use only a really thin plate to avoid a fluid in engine block ports (it take a lot of time to clean it properly), but a real torque plate is not a necessary in our stiff TC blocks.

I think that in US this type of boring is popular because an US engine builders works often with V8. In my opinion, this type of block are a less stiffer that our cast iron inline Fiat blocks. If I get in future an V8 block I will do a simillar test that today Fiat test and share with results here.

Sorry for poor quality of photos, I have today only my mobile phone, if somebody want I will make some better photos after weekend.

I am always happy to see people motivated to MEASURE, and not only assume and/or trust. Thumbs up! (My personal opinion, slight off-topic, hope GC won't mind: The latter got very widespread in the last decade, especially with many Internet "educated" backyard-tuners, out of whom the most can't answer a first "why", and the rest are brought to their knees by a second "why".)

To understand your results better, I have a couple of questions:

Was your second measurement with the cylinder head installed and torqued to specs (do you have some photos of the actual measurement)? Or after you removed the cylinder head again?

If the measurement had been performed with the cylinder head torqued, did you spot any deformation in upper part of the bore, measuring diameter virtually parallel to line connecting two diagonal head bolts?

Hi Nick, many thanks for your reply, I am really happy when I reading your post.

I done a bore diameter measurements with and without head to check how much TC block will change his shape when we assembled head to him. From my measurements I got that shape change is really minimal. The worst thing in my measurements is that I made it on a used bores, but I will do the same thing after reboring op will be done and share my results here.

I attached some photos here only for show members how I done it. If you need a really detailed "photostory" I will attach it here after reboring op, but heaven knows when I will do it. But, trust me, I will remeber about you and send you as much detailed photos as I can.

My friend Ernest and I are currently building an Integrale engine, to best of our knowledge and abilities. The agreed goal is to beat the best Integrale 1/4 mile time, but the real goal is to learn and have some good time while we do what we like the most (diagnosis: "motorheads and part-time humans"). To cut the long story short, we performed an analysis similar to yours.

However, there are a couple of differences between your and our engine block, their relevance varies, but for completeness, I listed most of them:

We have M12x1.25 head studs, while I believe you have OE thread M10x1.25

Tightening torque is higher than OE (to be honest, I am unsure how to compare it, due to torque-to-yield OE bolts and corresponding torquing specs)

Lower part of the coolant jacket has been filled with block filler

Mains caps are connected to block rails, by a strengthening steel plate (not installed during this operation)

Pistons have 84.42 mm nominal (& measured) diameter

"MLS" head gasket

There are also a few differences related to how the measurements were done. Here are our steps:

The bores pre-bored to 84.3 mm (without torque plate) to ensure the bores are round

The torque plate (incl. head gasket) torqued to specs

The block preheated to about 80 °C, by circulating hot water through the water jacket

Measurement set "A" (with torque plate and heated block) indicated presence of 4 "belly" regions, in plane 5 mm from the block deck. Consistently there was a deformation of 4-5/100 mm present. The deformation 40 mm from the block deck was minimal, 1-1.5/100 mm.
Measurement set "B" (heated block, without torque plate) indicated deformation of about 1/100 mm, in both planes.

Unfortunately, we have made too little effort to take photographic evidence of the measurements itself, being busy doing the work at the machine shop (having to pay their hourly rates, as effectively we were occupying a machine that could otherwise do some effective work).

In any case, some evidence is present (see the photo below). The final procedure was to bore, hone and flex-hone with preheated block and torque plate.

My block is fully stock spec now and I don't want to change a head bolts thread, in my engine this is not necessary.

I done my measurements without taking into account the effect of the temperature difference, I only checked how much TC block drift after head assembled to him.

I decided to make this thread to start a discuss with GC and GC site members and I am very glad that you Nick showed here your results, I am really appreciate.

Maybe before final boring op I will make first boring op to get a smaller bore size than final size, but I am fully of trust to GC words from his new book and I think that I wouldn't use a torque plate while I will doing a final boring op.

All very interesting indeed and I don't want to rain on anyone's parade. Nothing wrong with careful examination of things and certainly Nick I know you are highly professional in your approach to everything.

I will simply say this - the entire crankcase twists and deforms during full power operation. This is why crankshafts can develop a permanent 'set' in bending, the worst I have seen to date was 0.12mm - more than twice the allowable runout. Never had a seizure however - if the crank spins at build, it will keep spinning. Never had a piston seizure either.

I don't ask my supplier to use torque plates and I don't ask him to hot rebore! if I did I know what he'd say, and his credentials are second to none, approved engine rebuilder for Perkins, John Deere and many other top names.

Hmmm....a little more power and you understand how much metal twist in action...
Dragsters twist the crank (torsionally) so far (20 degrees in the big end of the track) that sometimes cam lobes are ground offset from front to rear to re-phase the valve timing somewhere closer to synchronization with the pistons.